This invention relates to a self centering device for maintaining a borescope in a centered position within a passage or conduit. More specifically it relates to an improved self centering device for maintaining a borescope in a centered position within a passage that accommodates itself to a wide range of inner passage diameters.
Borescopes are used for viewing inaccessible areas such as the interior portions of pipes of various kinds, jet engines, conduits in nuclear installations, and the like. Typically, borescopes comprise insertion tubes which are placed through an outlet of the region to be viewed, a light source for illumination, a means of conducting this illumination to the distal end (or head) of the insertion tube, an imaging device and optics for viewing a target positioned in the distal end of the insertion tube, an external video display monitor, and electronic circuitry for performing various necessary functions. When the target is remote from the outlet and, particularly when the route from the outlet to the target is not a linear one, a means of controlling the path taken by the insertion tube is also necessary.
When a borescope is being used for inspection of a long channel whose diameter is considerably wider than that of the borescope insertion tube, it is desirable to maintain the borescope in a centered position within the channel. Doing so serves two purposes. First the borescope head is protected from impact with or abrasion against obstacles in the channel. Second, the imaging function of the borescope is presented with the maximal visual field possible.
In order to allow a borescope to be used with a wide range of inner channel diameters, and also to travel in a channel whose internal diameter may change, as for example, where the channel comprises joined pipes of differing diameters, it is desirable that the borescope insertion tube operate in conjunction with a self centering apparatus. This device, used to center the borescope, must be capable of adjusting to different diameter channels as a route is traversed.
Wire spring elements are well suited for accomplishing this objective. If a portion of the distal section of a borescope is encased in a plurality of curved wire spring elements, a segment of each of these wire spring elements will engage the inner wall of the channel, and thus center the borescope head. Because the wire springs are resilient, they can be compressed to accommodate a smaller diameter passage, or expanded to accommodate a larger diameter passage. And where, as in the instant invention, one end of the self centering device is affixed at or near the borescope head and while the rest of the device is allowed to slide along the borescope insertion tube, the distance between the distal and proximate ends of the self centering device can be increased or shortened. If the distance is increased, the spring wire elements will describe a flatter arc and be accommodated to a smaller diameter channel. If the distance is decreased, the spring wire elements will describe a more rounded arc and be accommodated to a larger channel.
In the prior art, as for example in U.S. Pat. No. 4,418,572 to Prange and U.S. Pat. No. 2,587,476 to Huhn, the wire springs were secured at their ends to a collar. Thus, although some deformability was allowed, wide variations in conduit diameter placed severe strains on the spring wires, causing them to break prematurely. This breakage often happened in use, that is in the field, causing additional problems because the spring wires were welded or otherwise permanently affixed to the rest of the self centering device and could not be repaired or replaced in the field. Thus either spare centering devices had to be kept in the field, or else the entire operation had to be halted until the unit could be repaired off site and returned to the work site.